This section provides background information related to the present disclosure which is not necessarily prior art.
Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations that occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to the unsprung portion of the vehicle. The piston is connected to the sprung portion of the automobile through a piston rod which extends through the pressure tube.
The piston divides the pressure tube into an upper working chamber and a lower working chamber, both of which are filled with hydraulic fluid. Through valving, the piston is able to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended. Accordingly, the shock absorber is able to produce a damping force that counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle. In a dual tube shock absorber, a fluid reservoir or reservoir chamber is defined between the pressure tube and a reservoir tube. A base valve is located between the lower working chamber and the reservoir chamber to control the flow of fluid between the lower working chamber and the reservoir chamber.
Shock absorbers have been developed to provide different damping characteristics depending on the speed or acceleration of the piston within the pressure tube. Because of the exponential relationship between pressure drop and flow rate, it can be difficult to tune the damping characteristic of the shock absorber between low and high piston speeds. Specifically, the valving at the piston and/or base valve is designed to close/open in one unilateral movement, thereby causing an abrupt change in damping between low and high piston speeds.